A: Mastodon and GNU Social are /federated/ network with many individual servers. Only toots from profiles followed by someone on a given server propogate. "Follow Bots" ensure that more content is spread over more of the network. This may or may not be a good thing. And other bots may have other ideas. I'm not settled on the question myself.

Unlike previous followbots that actively follows everyone they find on other instances, this bot /passively/ wait for people from other instances to follow it, and then the bot will boost the "most popular" posts from those other instances.